The present invention relates to a procedure for examining and storing blood in bags. These bags are placed at the periphery of a circular disc. One or more discs may be placed one above the other, the discs inclined and then rotated so that the contents of the bags becomes thoroughly mixed. Each bag is allowed to pass a station, where a ray of light is directed towards a bag from below, the disc being provided with an aperture allowing the ray of light to reach the bag, pass the bag and then be received by a sensor after the ray of light has passed the bag. The light absorbed by the sensor is then conveyed to a computer for analysis.